Method of making separable matrices for seamless tooth-crowns.



Unirse STATES PATENT ortica SAMUEL o. sNYDER, or soRANToN, rnNNsrLvAnr;

METHOD OF MAKING SEPARABLE MATRICES FOR SEAMLESS TOOTH-CROWNL SPECIFICATION forming' part 0f Letters Patent N0. 655,525, dated August '7, 1900. Application led January 6, 1900. Serial No. 561. (No specimens.)

To all whom it may concern:

Be it known that I, SAMUEL C. SNYDER, a citizen of the United States, residing at Scranton, in the county of Lackawanna and State of Pennsylvania, have invented certain new and useful Improvements in Methods of Making Separable Matrices for Seamless Tooth- Crowns, of which the followingis a specification.

My invention relates to an improved method of making separable matrices to be used in the formation of seamless tooth-crowns. In the manufacture of matrices for this purpose it is at present customary to form an integral matrix by pouring into arnold a metal which is fusible at a low temperature, inserting a model tooth into the molten met-al, and then allowing the casting thus formed to cool. After the casting has cooled it is broken into two or more parts. On account of the difficulty experienced in separating the cold metal it is customary to form the casting with grooves in the sides, so that the lines of fracture will extend from the matrix to said grooves. For the purpose of making grooved castings a variety of devices have been designed. These consist of separable molds having webs or plates which extend radially inward toward the matrix and also of integral molds having removable plates which may-be placed therein prior to pouring the metal for the same purpose. In either case the result is unsatisfactory for se veral reasons. IVhen the webs or plates are used for the purpose of forming grooves in the casting, difficulty is experienced in freeing the plates from the casting, and in many instances the plates, as well as the casting, are damaged in effecting their removal. Furthermore, when the castings are broken while cold they are frequently splintered to such an extent as to render the matrix unlit for use. I have found that a separable matrix can be made in a much more satisfactory manner without the necessity of using special appliances for grooving the casting if a metal having the property of brittleness while hot is employed and said metal is struck or tapped lightly with a knife-edge after the metal has become set and before it has had time to cool. A greater percentage of perfect matrices can be obtained in this manner than by breaking the metal after it becomes cold, and the operation can be 'carried out in a much shorter time and with a great deal less trouble than where the process mentioned above is followed, 'as the metal splits with less difficulty and. less splintering when hot than when cold and it is unnecessary to free the casting from the grooving-plates.

In the accompanying drawings, Figures l to 6, inclusive, are perspective views illustratl ing my method of manufacturing the matv rices.

In carrying out my invention a mold, consisting of a tapering collar A, (shown in Figi 1,) is placed upon a metal block or anvil B and the molten metal C is poured into said mold. The block B forms a bottom for the mold and also conducts the heat away from the molten metal, so that the latter will set quickly. A model tooth D is inserted into the metal while the latter is still in its molten condition, and said tooth is held in place un-v til the metal becomes set. (See Fig. 2.) A metal suitable for the purpose consists of the following ingredients in the lfollowing proportions, by weight: tin, twenty-three parts; lead,nineteen parts; cad mium,thirteen parts, and bismuth, forty-eight parts. As soon as the metal solidiies it is forced out of the collar or mold and placed upon the block B. A knife E, having blades F, G, and H radiating in different directions from a central point and having a gap between the blades, as shown in Fig. 8, is then placed upon the top of the casting and struck lightly with a hammer or subjected to pressure before the cast'- ing has had time to cool. I have found that a very light stroke of the hammer when the metal is in a heated condition will cause the casting to split from top to bottom in straight lines, following the lines of compression between the knife-edges and the block. The casting separates into three pieces through the matrix without splintering, the adjoining faces of the parts being straight and clearly defined. Fig. 5 shows the separated parts, the tooth being removed, and Fig. t3 shows said parts replaced within the collaror mold and ready for use.

I have found that it is not even necessary to use a three-bladed knife, as the casting may IOO be separated by means of an ordinary knife I. (Shown in Fig. 4.) W'hen a plain knife-blade is used, it is laid upon the casting in a direction radiating from the tooth, as shown in said figure, and a light tap of the hammer will cause the casting to split in a straight line between the knife-edge and the block B and also to break in some other direction, following the line of least resistance from the matrix to the circumference, as indicated at J. If the tooth is not released by this division of the casting into two parts, the la-rger part, which retains the tooth, may again be divided in a similar manner if the casting be struck promptly before it has time to cool.

Owing to the fact that the castings have heretofore been separated while cool, it has been thought necessary to indent or groove them by pouring the metal around plates which are either formed integral with the mold or are made removable therefrom. In either event it isvnecessary to free the casting from the plates,' and this is sometimes a difficult matter, the plates and the casting frequently being broken in the process. After the plates are removed considerable force is required to separate the casting, and in so doing the matrix very frequently splinters and becomes useless.

It will be seen that my method oi' procedure is Very much simpler and more effective than the plan of operation generally employed and that no specially-designed molds are necessary. Thecastingsare moreperfectlyformed and with a great deal less trouble than is necessary with other processes, for reasons previously stated, and they can be made with much less metal than the castings which are formed with grooves in the sides, for the reason that with grooved castings a sufficient body of metal is left between the grooves and the matrix to form solid Walls for the latter, and the metal between the grooves is supertluous except for the purpose of forming walls for the grooves, so as to direct the lines of fracture, While a casting which is not grooved does not require any more metal than is suffieral use for making separable matrices, and

these compositions are all suitable for carrying out my process. I do not wish, therefore, to limit myself to the use of any specific composition.

Having described my invention, what I claim, and desire to secure by Letters Patent of the United States, is-

l. The method of making separable matrices for forming seamless tooth-crownswhich consists in placing within a mold a model tooth and a molten metal surrounding the tooth, said metal being fusible at a low temperature and having the property of brittleness While hot, allowing the metal to become set, then removing the casting thus made from the mold, then dividing the casting through the matrix while hot by compressing it between a blade and a suitable su pport, whereby said casting splits on the line of compression between the blade and the support.

2. The method of making separable matrices for forming seamless tooth-crowns which consists in placing Within a mold a modeltooth and a molten metal surrounding the tooth, said metal being fusible at a low temperature and having the property of brittleness while hot, allowing the metal to become set, then removing the casting thus made from the mold, and then splitting the metal while hot into three or more parts simultaneously on lines radiating from the matrix.

In testimony Awhereof I affix my signature in presence of Itwo witnesses.

SAMUEL C. SNYDER.

Witnesses:

ROBERT WATSON, FLORA LEVI. 

